I'll just park this here for future reference.
Sometimes you see writers say that certain parts of the Bible are written in the "apocalyptic" style of writing.
Recognising the "genre" of part of the Bible can be very important when it comes to reading it properly. For instance, parables and historical narrative communicate in very different ways; you'd completely misread the gospels if you confused them.
At the same time, identifying the genre is sometimes overrated. Some commentaries have a list of five or six ancient genres of writing, and they take many pages to discuss which best fits the passage in question. Often, in working out the overall message of that biblical passage, it makes very little difference exactly which bucket you put it in.
That said, what is "apocalypse"? I think this is a very helpful working definition. It comes from John J Collins' book, Apocalypse: The Morphology of a Genre (page 9), although I found it quoted in Lucas' commentary on Daniel (page 273):
…“a genre of revelatory literature with a narrative framework, in which a revelation is mediated by an otherworldly being to a human recipient, disclosing a transcendent reality which is both temporal, insofar as it envisages eschatological salvation, and spatial, insofar as it involves another, supernatural world.”
Lucas comments that Daniel 10-12 “are the one sub-section of the book of Daniel that fits this definition fully”.